The present invention relates to an integrated capacitor and a method for manufacturing an integrated capacitor. More specifically, a mechanically-adjustable capacitor is provided on a structure which may also include devices created by a complementary metal oxide semiconductor (xe2x80x9cCMOSxe2x80x9d) process. Micro-machined capacitors have been developed as part of micro-electro-mechanical systems. Using similar technologies to those used to manufacture semiconductors, microscopic capacitors may be fabricated on silicon wafers. These technologies may include oxidation of a substrate, application of a photoresist material, selective exposure to light or x-rays through a mask, and etching to build devices in layers on a substrate.
Although similar techniques are used for creating integrated circuits (xe2x80x9cICsxe2x80x9d)and micro-electro-mechanical devices (xe2x80x9cMEMsxe2x80x9d), when both ICs and MEMs are constructed on the same substrate, elements of these processes can interfere with each other. For example, polishing and etching processes used in the manufacture of ICs may damage MEMs that have already been created on a silicon wafer. In addition, subjecting certain MEMs to high temperatures used for processing and building MEMs can damage or destroy the CMOS. Cutting or xe2x80x9cdicingxe2x80x9d of a silicon wafer can also damage MEMs as stray particles can destroy a MEMs structure.
One solution for protecting a MEM during circuit creation and wafer processing has been to cover the MEM device with a protective layer (e.g., a layer of silicon oxide) during the processing stages in which the circuitry is created and the wafer is diced. This protective layer must later be removed in a time-consuming process. Furthermore, it is difficult to remove the protective layer without damaging the electronics components, and therefore the types of electronics that can be developed are limited.
Whether MEMs are developed first on a wafer and ICs are later developed, or the other way around, adding and later removing a protective covering for the first-developed components is generally required. These extra steps add time and expense to the process. Furthermore, in prior art processes, adding protective layers to cover components may be required to make the surface of the wafer approximately flat so that other operations such as etching and lithography may be performed.
These limitations have restricted the development of devices that include both MEMs and ICs. Such devices may include, for example, an adjustable capacitor and supporting circuitry that may, for example, be adapted to operate in a high-frequency antenna. When high-frequency antennas are adjusted to receive a certain frequency, the impedance of the antenna may be adjusted to reduce signal reflections. The impedance may be adjusted, for example, via adjusting the capacitance of an adjustable capacitor attached to the antenna. An adjustable capacitor can be used to compensate for the parasitic capacitance of the antenna circuitry.
Adjustable capacitors may be used to adjust antenna impedance, but integrated adjustable capacitors used for this application suffer from the manufacturing problems described above. Therefore, semiconductor diodes are frequently used for this application. Semiconductor diodes have a drawback that there is a large capacitance in the material of which they are constructed, thereby introducing a noise source into the system. An integrated adjustable capacitor that can be more easily manufactured on the same substrate as electronic circuits would be helpful for this application as well as several others, such as exact electrical filter, capacitor switches for radio frequency (RF) applications.